1. Field of the Invention
The present invention relates to a hollow needle for use in measurement of viscosity of liquids and, more particularly, a hollow needle for use in a device for measurement of viscosity of liquids which is easy to operate and makes it possible to measure the viscosity of a liquid in a very short time.
2. Description of the Prior Art
As is well-known, health conditions of a person have great influences on the viscosity of blood. In fact, the viscosity of blood of a person suffering from anemia, chronic renal insufficiency requiring hemodialysis, myocardial infarction, diabetes mellitus or malignant tumor, differs greatly from that of a person in normal health. In advanced nations, adult diseases such as, for example, myocardial infarction, thrombo-embolism and diabetes mellitus are increasing rapidly with increase in aged population. Thus, it can be said measurement of the viscosity of the blood is an important and effective factor essential for therapy and/or prevention of diseases.
So far, various devices have been developed to measure the viscosity of liquids or solutions. In the sphere of clinical medicine, however, there have been employed two devices, i.e., a capillary viscometer and a rotation viscometer. In the former, the viscosity of a liquid is measured by introducing the liquid into the capillary viscometer, and then causing the liquid to flow under external forces such as the gravitational force through a capillary or a fine tube of uniform bore to obtain the time required for its meniscus to pass through between predetermined levels. Such a capillary viscometer has been used widely to measure the viscosity of blood plasma. However, it is rarely the case that the capillary viscometers are applied to measure the viscosity of blood as the natural blood is non-Newtonian in its flow characteristics.
In order to determine the intrinsic viscosity, it is required to measure the viscosity several times using the same liquid and capillaries of varying diameter.
The measurement of the viscosity of bloods has generally been carried out with the rotation viscometers. A typical rotation viscometer comprises two concentric cylinders, the inner or outer cylinder being rotated in or rotated around the fixed outer or inner cylinder. In such a viscometer, the liquid is placed between two cylinders and either of the cylinders is rotated around its axis to measure its torque.
However, the rotation viscometers have the following disadvantages: (a) several measurements must be made on the same blood at different shear stresses in order to determine the intrinsic viscosity; (b) calculations are troublesome and lead to noticeable errors as they require graphical differentiation of logarithmic values by logarithmic values; (c) special and unstable flows such as Taylor vortex take place at high rotating rates; (d) the liquid to be examined generates heat by its viscosity; (e) there is a fear of causing deflection of blood corpuscles because of the centrifugal force; (f) the measurement for each specimen takes a long time; and (g) the viscometer is troublesome to handle as the viscometer must be cleaned every measurement by washing it with water and then drying the same to remove the blood adhered thereto.
To solve these problems, various new methods employing a roller pump system or a hollow fiber module have been proposed for measurement of the viscosity of blood. However, none of the viscometers of the prior art satisfies all the conditions required for application to the clinical medicine.
As is known, the blood is non-Newtonian in its flow characteristics, whereas the blood plasma behaves Newtonian. It is said, therefore, that the non-Newtonian behaviors of the blood result from the presence of blood corpuscles floating within the plasma. In particular, it is said that factors which have influences on the flow characteristics of the blood are the orientation of blood corpuscles and their various shapes such as disc shapes with concave surfaces, streamlined shapes or projectile shapes. The effect of such factors on the flow characteristics varies with a period of time elapsed from the blood collecting, and is affected by addition of other substances such as, for example, anticoagulants to the blood. Thus, it can be said that the best way to determine the flow characteristics of blood including its non-Newtonian behaviors is to select the blood circulating in the blood vessels of the body as the object of measurement.
However, there is no viscometer which makes it possible to directly measure the flow characteristics of the blood circulating in the blood vessels of the body. Thus, it is inevitable to use the collected blood as the object of measurement. In such a case, it is required to measure the flow characteristics of the blood correctly in the least time possible after blood-collecting, as well as to collect the blood without incorporating any other materials such as anticoagulants into the freshly drawn blood.
In addition, in order to adapt rheological blood tests to a routine clinical medicine, it is required to satisfy the following three conditions: (a) the measurement can be made with the natural blood; (b) the measurement can be made instantly at the bed side; and (c) the viscometer is easy to operate and operable for any person.
To solve these problems, it has been proposed in Japanese patent application No. Heisei 2-418855 to use a device for measurement of viscosity of liquid, comprising an evacuated vessel composed of a hollow cylinder and a pair of stoppers provided at both ends of the cylinder to keep a lowered pressure of the vessel, a hollow needle adapted to be pierced into one of the stoppers to let it go into the vessel, a pressure sensor for detecting an internal pressure of the vessel, a connecting needle pierced into the other stopper to communicate the pressure sensor with the interior of the vessel, and a means for calculating the viscosity of a liquid from change of the internal pressure of the vessel. This device is easy to operate and makes it possible to correctly and rapidly measure the viscosity of a liquid with a small amount of the liquid.
In such a device, the liquid to be measured in the liquid container is introduced into the vessel through the hollow needle by the difference between the internal pressure of the evacuated vessel and the atmospheric pressure acting on the surface of the liquid in the container. In order to put such a device into practical use, it is required to develop an inexpensive hollow needle which can be mass produced with ease.